Originally Posted by DaveSSS

If you compare the stack and reach values to the old fashioned method of comparing the TT length, with corrections for the STA, both methods suggest that the XL has a 1.8-1.9mm longer reach than the L. What's unlikely is that the stack on XL is only 2.3cm greater that the size L. That would require a significantly lower BB height. Most likely, that stack height difference is 3.3cm.

You can't compare the reach values of frames with different stack heights, directly. To make a proper comparison, the reach of the smaller frame should be corrected to the same height as the larger one. That correction requires subtracting 3mm from the reach for each 10mm of stack height difference. That makes the smaller frame's reach shorter and the difference larger. The assumption is that both frames would be setup with the same total stack, using more spacers on the smaller frame. A frame shouldn't force a rider to adopt an undesired position.